Need help trying to pass a member function of another class into a std::function parameter

I have a class with a function that takes a std::function and stores it. This part seems to compile ok (but please point out any issue if there are any)

class worker
{
   std::function<bool(std::string)> m_callback;
   void do_work(std::function<bool(std::string)> callback)
   {
      m_callback = std::bind(callback, std::placeholders::_1);
      callback("hello world\n");
   }
};

Now I have my main and another "helper" class where I want to call this above function and pass in a function from the helper class to it:

// pretty boring class - a cut down of my actual class
class helper
{
   worker the_worker;
   bool work_callback(std::string str)
   {
      std::cout << str << std::endl;
   }
}

int main
{
   helper the_helper;
   the_worker.do_work(std::bind(&helper::work_callback, the_helper, std::placeholders::_1));  // <---- SEGFAULT
}

Note: hand copied code, so there might be a type-o in here... please forgive!

I get a segfault, but I am not sure why :( I have used this before, in fact I copied this example from another place I used it. The only real difference that that the member function was part of the class I called it from (i.e. this instead of the_helper).

So this is why I am also asking if there is anything else I am doing wrong in general? Like should I be passing the std::function as:

void do_work(std::function<bool(std::string)>&& callback)

or

void do_work(std::function<bool(std::string)>& callback)